192 IODP-ICDP Expedition 364 to the Chicxulub Impact Crater

Tuesday, 24 October 2017
8:00 AM - 12:00 PM
Ballroom 6A

ISOLATED DEEP-WATER MAASTRICHTIAN PLANKTONIC FORAMINIFERS OF THE RESURGE BRECCIA AND SETTLING LAYER OF IODP-ICDP EXP364 HOLE M0077A IN THE CHICXULUB CRATER

Paper number: 192-9
Program: Technical Sessions
Time: 10:25 AM – 10:45 AM

Authors

Abstract

Hole M0077A was drilled on the peak ring of the Chicxulub structure. Therefore the late and post-impact crater infill on the ring was not influenced by lateral sediment input like the Yax-1 core. On top of the shocked basement the direct fall-out breccia from cores 87-53 is followed by graded resurge infill from core 53 to core 40-1-110cm. A 78 cm thick graded laminated transitional interval (1G) from 40-1-110cm to 40-1-32cm has presumably settled from the turbulent waters in the waning stages of the crater basin seiche, sharply overlain by basal Paleocene background infill of marly wackestones of the P0-Pa zone. Like earlier recovered samples of the Chicxulub impact breccia (Yuc-6, Yax-1) many limestone clasts occur with enclosed foraminifers, and up-section increasing amounts of isolated benthic and planktonic foraminifers were recovered from the resurge breccias of the Chicxulub drillhole. In the basal fall-back breccia (cores 86-40) already large carbonate platform and deepwater limestone clasts were found containing a variety of upper Cretaceous large benthic foraminifers, miliolids, rudist fragments. These clasts demonstrate -perhaps surprisingly- few shock features. Upsection (cores 45-40) the amount of isolated Maastrichtian planktonic foraminifers (among others G. stuarti, C. contusa aff, heterohelicids) increases. These foraminifers are quite well preserved displaying details of the wall structure. The sub-thermocline dwelling large globotruncanids demonstrate that before the impact on the Yucatan carbonate platform a deep-water area existed, presumably the gravity low in the north1. The presence of the well preserved foraminifers probably explains the earlier interpretation of a Maastrichtian age of the crater infill2. These occurrences are documented on core-logs of Pemex, in a lithology that was not recognized as part of the impact lithologies, but regarded as background crater infill.

1Gulick et al. 2008, Nature Geoscience, 1,131. 2Ward et al 1995, Geology, 23,873.

Co-authors: IODP-ICDP Expedition 364 Scientists

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-302277

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